Cache Status Value Locking for Exclusive Operation Delays
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Solution Overview
Problem
In data processing apparatuses with caches, the execution of load-exclusive and store-exclusive operations can be disrupted by cache management mechanisms, leading to delays in store-exclusive operations due to potential modifications in status values indicating non-exclusive usage.
Innovation Solution
The data processing apparatus prevents modification of status values for a predetermined time period after a load-exclusive operation, ensuring that store-exclusive operations can complete quickly by prioritizing and stalling relevant instructions and locking cache access as necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the cache management mechanisms operate independently to maintain status values for local copies, then the cache can efficiently manage data values, but the store-exclusive operation may be delayed due to modifications in status values
Solution Approach 1:
The patent applies preliminary anti-action by preventing modification of the status value in advance before the store-exclusive operation executes. When a load-exclusive operation is detected, the system proactively blocks any cache management mechanism from modifying the status value of the associated local copy, thereby eliminating potential delays before they can occur.
Solution Approach 2:
The system performs preliminary action by identifying and locking the status value associated with a local copy immediately upon detecting a load-exclusive operation. This preliminary locking ensures that when the subsequent store-exclusive operation executes, the status value is already protected and ready, avoiding any waiting time during the actual store operation.
2Reliability
If the status value is allowed to be modified by cache management mechanisms, then the cache can accurately track exclusive usage status, but the store-exclusive operation cannot complete quickly
Solution Approach 1:
The patent introduces an intermediary mechanism that mediates between the cache management system and the load-exclusive/store-exclusive operations. This intermediary monitors and controls access to the status value, allowing cache management to maintain accuracy while blocking modifications that would interfere with the exclusive operation sequence, thus satisfying both reliability and speed requirements.
Solution Approach 2:
The system dynamically adjusts the status value modification permissions based on the operational context. When a load-exclusive operation is active, the status value becomes immutable; when no such operation is pending, normal cache management modifications are permitted. This dynamic behavior ensures both accurate tracking and fast operation completion.
3Reliability
If the store-exclusive operation waits for cache management to complete, then data consistency is maintained, but the operation speed decreases
Solution Approach 1:
The patent extracts the status value protection mechanism from the general cache management flow. Instead of requiring the store-exclusive operation to wait for complete cache management cycles, the system selectively extracts and protects only the specific status value associated with the local copy involved in the exclusive operation, maintaining consistency for that specific data while allowing other cache operations to proceed independently.
Data Source
AI summary
A data processing apparatus is provided in which a processor unit accesses data values stored in a memory and a cache stores local copies of a subset of the data values. The cache maintains a status value for each local copy stored in the cache. When the processor unit executes a load-exclusive operation, a first data value is loaded from a specified memory location and an exclusive use monitor begins monitoring the specified memory location for accesses. When the processor unit executes a store-exclusive operation, a second data value is stored to the specified memory location if the exclusive use monitor indicates that the first data value has not been modified since the load-exclusive operation was executed. When a local copy of the first data value is stored in the cache and the status value for the local copy of the first data value indicates that the processor unit has exclusive usage of the first data value, the data processing apparatus is configured to prevent modification of the status value for a predetermined time period after the processor unit has executed the load-exclusive operation.